1. Field of the Invention
The present invention is related to a device for demineralizing water, especially in order to reduce its hardness.
2. Discussion of Background Information
Water hardness, represented by a water hardness testing level or TH, which is expressed in degrees Fahrenheit (.degree.F.), measures the concentration of various calcium and magnesium salts. We are aware of a comprehensive list of salts that determine water hardness, especially by the publication "Memento technique de l'eau" Ninth Edition 1989, page 485, Editions Degremont. The main characteristic of these salts is to co-precipitate if the temperature is raised, especially beyond approximately 60.degree. C., and to form deposits, commonly known as tartar. Water treatment, in order to reduce its hardness, often consists of fighting tartar, although other aims can also be undertaken, such as for example demineralizing water for laboratory applications.
A variety of devices for the partial or total demineralization of water, especially in order to reduce its hardness, are currently known. Among the most commonly used devices, one can differentiate between those using ion exchange resins, and those that function by precipitation, either by adding a precipitating agent, or by raising temperature.
We are also aware of devices that prevent tartaring, in which a magnetic field is created that stops the formation of precipitates. However, these devices do not enable the reduction of the quantity of minerals contained in the water, and therefore to reduce its hardness.
In devices using ion exchange resins, water is made to pass through a granular resin that retains the salts by an ionic exchange, and water is captured at its exit. These devices are remarkably efficient, although efficiency decreases rapidly as the resin is saturated by salts. Some resins can be regenerated, and this substantially increases their life span. However, the resins/used have some disadvantages. On the one hand, they are expensive and on the other hand, they have a short life span, except in cases of regeneration. However, regeneration is both long and pain-staking.
In devices functioning by precipitation, a precipitating agent is added causing a selective precipitation of salts and then the precipitates formed are eliminated. Relatively simple, and less expensive, these devices however have certain disadvantages. For example, the introduction of a precipitating agent requires obtaining a very precise measurement of the salts to be precipitated, and one runs the risk of either introducing too little agent in order to precipitate the totality of the salts, or, on the contrary, of introducing too much, necessitating the elimination of such excess precipitating agent. Additionally, the precipitating agent does not act on the totality of the salts, and some of these, which influence water hardness, generally remain present in the water after its treatment. Moreover, the removal of the precipitate formed by the precipitating agent requires the implementation of fairly complex devices necessitating frequent maintenance.
In devices functioning by precipitation by raising the temperature of the water to be demineralized, such water is made to pass along a hot surface, which causes, on such surface, a precipitation of numerous salts. Prevention of tartar deposits in industrial boilers is often obtained in this manner.
These devices, that are relatively simple to implement, suffer, however, from the fact that their reliability is uncertain, and their efficiency is fairly limited. Indeed, the precipitates that accumulate on the hot surface form, in general, quasi-impermeable, extremely dense and extremely hard deposits, that rapidly reduce the efficiency of the heat transfer surface of the hot surface. In addition, the homogenous heating of water can only be obtained with difficulty, because the upper layer of the water is not in contact with the hot surface. The result is that either only one portion of the water is demineralized, or that precipitation is spread out spatially, resulting in the creation of overwhelming deposits that are badly located.
Suggestions have been made to improve the efficiency of devices for precipitating salts by heat effect by increasing the area of the hot surface with which the water to be treated comes into contact. Thus, in the patent HULSMEYER DE-C-363 253, the water to be treated is introduced at the upper portion of a closed cylindrical enclosure having a vertical axis and containing a porous material of a truncated shape, which extends along the greater portion of the height of the enclosure, and is constituted of tough or synthetic stone. This material is heated by injection, in the enclosure, of pressurized steam. The water to be treated flows both on the external surface of the porous material, between the chinks separating the different blocks, and through the volume of the porous material itself with a lesser through-put. Such a devices has substantial inconveniences.
First, the quality of the demineralization obtained is not uniform because, as is clear, it depends on the throughput of water brought to the surface of the porous material. In fact, the greater this through-put and the greater the quantity of water that flows outside the porous material, the greater is the proportion of water that does not come into contact (or very little contact) with the porous material.
Second, such a device is especially cumbersome, and this excludes it from being used in various applications and especially, for small utilitarian appliances, such as irons, wallpaper removers, etc.
Generally speaking, demineralizing devices belonging to prior art and using heated porous materials, crossed by the water to be demineralized, have two major disadvantages that manifest themselves and worsen with increased use by a progressive blocking of the pores due to the formation of quasi-impermeable deposits mentioned previously. First, the through-put is substantially limited, and second, reducing the contact surface of the water with the porous material results in a drop in the quality of the demineralization as it is used.